1. Field of the Invention
A toroidal-type continuously variable transmission and a continuously variable transmission apparatus according to the invention are used as an automatic transmission apparatus for a vehicle or a transmission apparatus for adjusting the operating speed of various industrial machines such as a pump.
2. Description of the Related Art
As an example of a transmission which constitutes a transmission for a vehicle, there is known a toroidal-type continuously variable transmission; and, use of such toroidal-type of continuously variable transmission is enforced in part of the vehicle industry. The thus partly enforced toroidal-type continuously variable transmission is a toroidal-type continuously variable transmission of a so called double cavity type in which transmission of power from an input part to an output part is carried out using two systems disposed in parallel to each other. While a toroidal-type continuously variable transmission of this type is conventionally known because it is disclosed in a large number of publications such as U.S. Pat. No. 5,033,322, U.S. Pat. No. 5,569,112 and U.S. Pat. No. 5,651,750, description will be given below of the basic structure of toroidal-type continuously variable transmission of this type with reference to FIG. 7.
A toroidal-type continuously variable transmission shown in FIG. 7 has an input rotary shaft 1 which corresponds to a rotary shaft. On the peripheries of the near-to-middle-portion-base-end portion (in FIG. 7, the near-to-left-side portion) and the near-to-leading-end portion (in FIG. 7, the near-to-right-side portion) of the input rotary shaft 1, there are supported two input side disks 2a, 2b which correspond to outside disks, respectively. These two input side disks 2a, 2b are respectively supported through their associated ball splines 4, 4 on the input rotary shaft 1 in a state where their input side surfaces 3, 3, which are the axial-direction one-side surfaces of the input side disks and are formed as toroid curved surfaces, are disposed opposed to each other. Therefore, the two input side disks 2a, 2b are supported on the periphery of the input rotary shaft 1 in such a manner that they can be shifted in the axial direction of the input rotary shaft 1 and can be rotated in synchronization with the input rotary shaft 1.
Also, between the base end portion (in FIG. 7, the left end portion) of the input rotary shaft 1 and the outer surface of the input side disk 2a, there are interposed a rolling bearing 5 and a pressing device 6 of a loading cam type. And, a cam plate 7, which constitutes the pressing device 6, is disposed in such a manner that it can be driven and rotated by a drive shaft 8. On the other hand, between the leading end portion (in FIG. 7, the right end portion) of the input rotary shaft 1 and the outer surface of the other input side disk 2b, there are interposed a loading nut 9 and a countersunk plate spring 10 having large elasticity.
The middle portion of the input rotary shaft 1 is inserted through a penetration hole 13 which is formed in a partition wall portion 12 disposed within a casing 11 (see FIGS. 1 to 3, 5 which show the mode for carrying out the invention) in which the toroidal-type continuously variable transmission. A cylindrical-shaped output cylinder 28 is rotatably supported on the inside diameter side of the penetration hole 13 by a pair of rolling bearings 14, 14, while an output gear 15 is fixed to the outer peripheral surface of the middle portion of the output cylinder 28. Also, on such portions of the two end portions of the output cylinder 28 that respectively project from the two outer surfaces of the partition wall portion 12, there are supported two output side disks 16a, 16b corresponding to inside disks by spline engagement in such a manner that they can be rotated in synchronization with the output cylinder 28
In this state, the output side surfaces 17, 17 of the output side disks 16a, 16b, which are the axial-direction two side surfaces of the output side disks and are respectively formed as toroid curved surfaces, are disposed opposed to the respective input side surfaces 3, 3. Also, between the outer peripheral surface of the middle portion of the input rotary shaft 1 and such portions of the inner peripheral surfaces of the two output side disks 16a, 16 that project beyond the end edge of the output cylinder 28, there are interposed needle roller bearings 18, 18, respectively. While supporting the loads to be applied to the two output side disks 16a, 16b, the output side disks 16a, 16b can be rotated and shifted in the axial direction with respect to the input rotary shaft 1.
Also, on each of such portions of the periphery of the input rotary shaft 1 that are present between the input and output side surfaces 3, 17 (cavities), there are disposed a plurality of (generally, two or three) power rollers 19, 19. These power rollers 19, 19 respectively include peripheral surfaces 29, 29 which are respectively formed as spherically projecting surfaces to be contacted with the input and output side surfaces 3, 17; and, the power rollers 19, 19 are respectively supported on the side surface portions of trunnions 20, 20 serving as support members by displacement shafts 21, 21, radial needle roller bearings 22, 22, thrust ball bearings 23, 23 and thrust needle roller bearings 24, 24 in such a manner that they can be rotated and can be swung and shifted slightly. That is, the displacement shafts 21, 21 are respectively shafts of an eccentric type which are structured such that their respective base half sections and front half sections are eccentric to each other; and, of the two half sections of the displacement shafts 21, 21, the base half sections are respectively supported on the middle portions of the trunnions 20, 20 by another radial needle roller bearings (not shown) in such a manner that they can be swung and shifted.
The power rollers 19, 19 are rotatably supported on the front half sections of the thus-structured displacement shafts 21, 21 by the radial needle roller bearings 22, 22 and thrust ball bearings 23, 23. Also, the shifting movements of the power rollers 19, 19 with respect to the axial direction of the input rotary shaft 1 based on the elastic deformation of the respective composing parts of the toroidal-type continuously variable transmission are allowed due to the-above-mentioned another radial needle roller bearings and thrust needle roller bearings 24, 24.
Further, the trunnions 20, 20 support the pivot shafts 32, 32 (see FIG. 3 which shows the mode for carrying out the invention), which are disposed on the two end portions (in the front and back direction in FIG. 7) of the trunnions 20, 20, on support plates 25a, 25b (see FIGS. 1 to 4 which show the mode for carrying out the invention) which are installed within the casing 11, in such a manner that the pivot shafts 32, 32 can be swung as well as can be shifted in the axial direction. That is, not only the trunnions 20, 20 are supported in such a manner that they can be swung and shifted clockwise and counterclockwise in FIG. 7, but also they can be shifted in the axial direction (in FIGS. 1 to 4, in the upward and downward directions; and, in FIG. 7, in the front and back direction) of the pivot shafts 32, 32 by actuators 31, 31 of an oil pressure type (see FIG. 3 which also shows the mode for carrying out the invention) stored in an actuator body 30 (see FIGS. 1 to 4 which show the mode for carrying out the invention).
When the above-structured toroidal-type continuously variable transmission is in operation, the input side disk 2a can be driven and rotated by the drive shaft 8 through the pressing device 6. Since the pressing device 6 drives and rotates the input side disk 2a while generating an axial-direction thrust force, the pair of input side disks 2a, 2b including the above-mentioned input side disk 2a are respectively pushed toward their associated output side disks 16a, 16b are also rotated in synchronization with each other. As a result of this, the rotational movements of the two input side disks 2a, 2b are respectively transmitted through their associated power rollers 19, 19 to their associated output side disks 16a, 16b, thereby rotating the output gear 15 which is connected to the respective output side disks 16a, 16b through the output cylinder 28.
When the present toroidal-type continuously variable transmission is in operation, the surface pressures of the respective contact portions between the peripheral surfaces 29, 29 of the power rollers 19, 19 and the input and output side surfaces 3, 17 can be secured by the thrust force to be generated by the pressing device 6. Also, these surface pressures increase as the power (torque) to be transmitted from the drive shaft 8 to the output gear 15 increases. Therefore, there can be obtained good transmission efficiency regardless of variations in the torque. Also, even in case where the torque to be transmitted is 0 or quite small, the surface pressures of the contact portions can be secured to a certain degree by the countersunk plate spring 10 and a pre-load spring 26 which is disposed on the inside diameter side of the pressing device 6. Accordingly, the torque transmission in the contact portions can be carried out smoothly without incurring excessive slippage even immediately after start of the operation of the toroidal-type continuously variable transmission.
To change the transmission ratio between the drive shaft 8 and output gear 15, the trunnions 20, 20 may be shifted in the front and back direction in FIG. 7 by the actuators 31, 31 (see FIG. 3). In this case, the trunnions 20, 20 in the upper half section in FIG. 7 and the trunnions 20, 20 in the lower half section in FIG. 7 are shifted by the same amount but in the mutually opposite directions. Such shifting motion changes the directions of the forces to be applied in the tangential directions of the contact portions between the peripheral surfaces 29, 29 of the power rollers 19, 19 and the input and output side surfaces 3, 17. And, due to the tangential-direction forces, the trunnions 20, 20 are swung about the pivot shafts 32, 32 that are disposed on the two end portions of their associated trunnions 20.
Such swinging motion of the trunnions 20 changes the positions of the contact portions between the peripheral surfaces 29, 29 of the power rollers 19, 19 and the input and output side surfaces 3, 17 with respect to the diameter directions of the side surfaces 3, 17. The more the contact portions shift outwardly in the diameter direction of the input side surface 3 and inwardly in the diameter direction of the output side surface 17 respectively, the more the transmission ratio changes to the speed increasing side. On the other hand, as shown in FIG. 7, the more the above contact portions changes inwardly in the diameter direction of the input side surface 3 and outwardly in the diameter direction of the output side surface 17 respectively, the more the transmission ratio changes to the speed reducing side.
In the case of the conventional structure shown in FIG. 7, the output cylinder 28 is rotatably supported on the partition wall portion 12, the pair of output side disks 16a, 16b are respectively disposed on the two sides of the partition wall portion 12, and the power rollers 19, 19 are also respectively disposed on the two sides of the partition wall portion 12. This arrangement makes it troublesome to assemble the support plates 25a, 25b and trunnions 20, 20 and the like into the casing 11. That is, to assemble the toroidal-type continuously variable transmission into the casing 11, after the support plate 25a situated on the deep side (in FIGS. 1 and 2, on the upper side) of the casing 11 is assembled to the casing 11 and the output cylinder 28 is assembled to the partition wall portion 12, with the pair of output side disks 16a, 16b assembled to the output cylinder 28, the input rotary shaft 1 must be inserted and further the four trunnions 20, 20, the support plate 25b on the actuator body 30 side (in FIGS. 1 and 2, on the lower side), the actuator body 30 and the pair of input side disks 2a, 2b must be assembled sequentially in this order.
The above assembling operation of the respective composing parts of the conventional structure must be carried out in a limited (small) space which is present within the casing 11 and thus the assembling operation is troublesome. Also, in case where a poor operation is found in any one of the composing parts due to the errors of the dimensions of the parts and poor assembled conditions after they are assembled, it is also troublesome to cope with such poor operation. That is, in order to allow the toroidal-type continuously variable transmission to fulfill its expected performance, the position relationships between the composing parts must be restricted very strictly and, after assembled, it is necessary to make measurements as to whether the position relationships between the respective composing parts are accurate or not as well as whether the respective composing parts operate accurately or not. In case where this measuring operation finds any poor operation in the composing parts, the composing parts assembled must be dismantled and, as the need arises, the composing parts must be assembled again by changing the parts to be assembled (for example, by changing a shim for dimension adjustment). These dismantling and re-assembling operations must be respectively carried out in a limited space within the casing 11, which is troublesome. Especially, in the case of a continuously variable transmission apparatus in which a toroidal-type continuously variable transmission and a planetary gear mechanism are combined together in order to increase the transmission ratio and enhance the durability and transmission efficiency, the number of parts to be assembled is large, which causes the above-mentioned problems to arise more often.
Further, in the case of the conventional structure shown in FIG. 7, since, between the outer surfaces 27, 27 of the pair of output side disks 16a, 16b, there are interposed not only the output gear 15 but also the pair of rolling bearings 14, 14 and the partition wall portion 12 for supporting these rolling bearings 14, 14, the distance D27 between the two outer surfaces 27, 27 is large. This large distance increases the axial-direction dimension of the toroidal-type continuously variable transmission, so that the toroidal-type continuously variable transmission increases in size and weight. Such increases in the size and weight of the toroidal-type continuously variable transmission are caused not only by the increase in the distance D27 but also by increases in the axial-direction thicknesses of the respective output side disks 16a, 16b. The reason for this as follows.
That is, in the speed reducing state of the toroidal-type continuously variable transmission shown in FIG. 7, the peripheral surfaces 29, 29 of the power rollers 19, 19 press against the output side surfaces 17, 17 of the output side disks 16a, 16a in a state where these peripheral surfaces 29, 29 are contacted with the near-to-outside-diameter portions of these output side surfaces 17, 17. As a result of this, large moments, the centers of which are the spline engaged portions thereof with the output cylinder 28, are applied to the output side disks 16a, 16a. In order to restrict a deviation in the transmission ratio and secure the durability of the output side disks 16a, 16b regardless of such large moments, the elastic deformation of these output side disks 16a, 16b must be restricted. And, to restrict such elastic deformation, it is necessary to increase the axial-direction thickness dimensions of the output side disks 16a, 16b to thereby enhance the rigidity of the output side disks 16a, 16b. However, in case where the axial-direction thickness dimensions of the output side disks 16a, 16b are increased for this reason, as described above, the toroidal-type continuously variable transmission increases in size.
On the other hand, in JP-2001-116097, there is disclosed a structure in which an output side disk of an integral type is rotatably supported on the periphery of the middle portion of an input side rotary shaft by a pair of radial needle roller bearings and a pair of thrust needle roller bearings. According to this structure, not only the partition wall portion 12 can be omitted from the conventional structure shown in FIG. 7 but also dimension of the output side disk in a axial direction thereof can be shortened, therefore a toroidal-type continuously variable transmission can be reduced in size and weight as a whole. However, in the case of the structure disclosed in the above-cited publication JP-2001-116097, no consideration is given to the facilitation of an assembling operation.